1. Field of the Invention
The present invention generally relates to control of working fluid flow and, more particularly, is concerned with a flow control valve construction employing a unique readily replaceable cartridge subassembly.
2. Description of the Prior Art
Flow control valves having a housing or body with a central bore in which a spool is slidable longitudinally between various working and/or neutral positions are well known in the prior art. Representative of the prior art are the flow control valves disclosed in U.S. Pat. Nos. to Hodgson et al (3,481,364), Sugden, Jr. (3,596,679), Stiltner (3,763,891) and Richter et al (4,388,946). One typical conventional valve is the four-way valve exemplified by Stiltner wherein the valve body has a pair of pressure and return ports and a pair of working ports. Also, the valve slide or spool is spring loaded to a neutral center position and actuatable to right or left of center working positions. In the neutral center position, fluid from a source is conducted via the pressure port to the return port, bypassing the pair of working ports. In the right of center working position, fluid is conducted via the pressure port to one of the working ports and then returned via the other working port to the return port. On the other hand, in the left of center working position, just the opposite occurs, namely, fluid is conducted via the pressure port to the other working port and then returned via the one working port to the return port.
One common shortcoming of conventional flow control valves, as also exemplified by Stiltner, is that their various constructions do not facilitate quick and easy repair and maintenance in the field. Typically, in order for repair or replacement of their components to be carried out, they have to be removed from service. For instance, such procedure would be necessary in the case of the Stiltner valve in view of the multiplicity of parts which must be removed and accounted for in disassembling the valve.
Consequently, a need exists for improvements in flow control valve construction which will eliminate this shortcoming without, at the same time, offsetting the benefits to be derived therefrom by increasing overall cost of the valve.